package org.apache.lucene.search.spans;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

import org.apache.lucene.search.Explanation;
import org.apache.lucene.search.Weight;
import org.apache.lucene.search.Scorer;
import org.apache.lucene.search.Similarity;

/**
 * Public for extension only.
 */
public class SpanScorer extends Scorer {
    protected Spans spans;
    protected byte[] norms;
    protected float value;

    protected boolean more = true;

    protected int doc;
    protected float freq;

    protected SpanScorer(Spans spans, Weight weight, Similarity similarity, byte[] norms) throws IOException {
        super(similarity, weight);
        this.spans = spans;
        this.norms = norms;
        this.value = weight.getValue();
        if (this.spans.next()) {
            doc = -1;
        } else {
            doc = NO_MORE_DOCS;
            more = false;
        }
    }

    @Override
    public int nextDoc() throws IOException {
        if (!setFreqCurrentDoc()) {
            doc = NO_MORE_DOCS;
        }
        return doc;
    }

    @Override
    public int advance(int target) throws IOException {
        if (!more) {
            return doc = NO_MORE_DOCS;
        }
        if (spans.doc() < target) { // setFreqCurrentDoc() leaves spans.doc() ahead
            more = spans.skipTo(target);
        }
        if (!setFreqCurrentDoc()) {
            doc = NO_MORE_DOCS;
        }
        return doc;
    }

    protected boolean setFreqCurrentDoc() throws IOException {
        if (!more) {
            return false;
        }
        doc = spans.doc();
        freq = 0.0f;
        do {
            int matchLength = spans.end() - spans.start();
            freq += getSimilarity().sloppyFreq(matchLength);
            more = spans.next();
        } while (more && (doc == spans.doc()));
        return true;
    }

    @Override
    public int docID() {
        return doc;
    }

    @Override
    public float score() throws IOException {
        float raw = getSimilarity().tf(freq) * value; // raw score
        return norms == null ? raw : raw * getSimilarity().decodeNormValue(norms[doc]); // normalize
    }

    @Override
    public float freq() throws IOException {
        return freq;
    }

    /** This method is no longer an official member of {@link Scorer},
     * but it is needed by SpanWeight to build an explanation. */
    protected Explanation explain(final int doc) throws IOException {
        Explanation tfExplanation = new Explanation();

        int expDoc = advance(doc);

        float phraseFreq = (expDoc == doc) ? freq : 0.0f;
        tfExplanation.setValue(getSimilarity().tf(phraseFreq));
        tfExplanation.setDescription("tf(phraseFreq=" + phraseFreq + ")");

        return tfExplanation;
    }

}
